1. Technical Field
The present invention relates generally to predicting yield in VLSI designs, and more specifically relates to a system and method that predicts yield by categorizing and analyzing sub-circuits contained in the VLSI design.
2. Related Art
An important step in the VLSI (very large scale integrated circuit) design process involves predicting manufacturing yield. Manufacturing yield refers to the ratio of good versus defective devices that result during a manufacturing process. Accurately predicting the manufacturing yield ahead of time allows the designers to head off low yielding chip designs prior to any costly manufacturing processes.
There are two traditional models for manufacturing yield prediction of VLSI designs: the circuit model and the critical-area model. The circuit model uses the schematic of a design to produce an estimate based on counts of devices and size and type of embedded memory arrays (see, e.g., C. H. Stapper, J. A. Patric, and R. J. Rosner, “Yield Model for ASIC and Processor Chips,” IEEE Workshop on Defect and Fault Tolerance in VLSI Systems, Venice, Italy, Oct. 27-29, 1993). The critical-area model uses geometric analysis of the physical design, independent of circuit function, to produce a yield estimate (see, e.g., C. H. Stapper, “Modeling of Integrated Circuit Defect Sensitivities,” IBM Journal of Research and Development, Vol. 27, No. 6, November, 1983).
There is a clear need for the ability to refine the circuit-area model by using actual yield estimates from the layout shapes corresponding to different circuit types in the circuit yield model. Because existing approaches require an engineer to subset the chip content into separate pieces to be analyzed, it is extremely laborious to collect enough data to be statistically acceptable. Thus, the number of categories of circuits and functions is forced to be small so it is manageable; and therefore, the accuracy of a yield estimate from critical area analysis and scaling could be increased if a better way to perform such analysis existed.